Method for prolonging the life of refractory linings in furnaces of the kaldo, linz-donowitz, de may or basic or acid converter types



Nov. 7, 1967 R. .1. DEMAISON 3,351,460

METHOD FOR PROLONGING THE LIFE OF REFRACTORY LININGS IN FURNACES OF THE KALDO, LINZ-DONOUIITZ, DEMAY 7 OR BASIC OR ACID CONVERTER TYPES Filed Jan. 7, 1965 5 Sheets-Sheet 1 INVENTOR. 1?. (Z flEMA/so/v No'v. 7, 1967 R. J. DEMAISON 0 METHOD FOR PROLONGING THE LIFE OF REFRACTORY LININGS 1N FURNACES OF THE KALDO, LINZ-DONOWITZ DEMAY OR BASIC OR ACID CONVERTER TYPES Filed Jan. 7, 1965 5 Sheets-Sheet 2 INVENTOR. F 0EMA/SOIV N 1967 R. J. DEMAISON 3,351,460

METHOD FOR PROLONGING THE LIFE OF REFRACTORY LININGS 1N FURNACES OF THE KALDO, LINZ-DONOWITT-, DEMAY 0R BASIC OR ACID CONVERTER TYPES Filed Jan. 7, 1965 5 Sheets'-Shet 5 INVENTOR: fi DEMAISGN WWW 15 1" ORN Nov. 7, 1967 R. J. DEMAISON 3,351,460

METHOD FOR PROLONGING THE LIFE OF REFRACTORY LININGS 1N FURNACES OF THE KALDO, LINZ-DONOWITZ, DEMAY on BASIC on ACID CONVERTER TYPES 5 Sheets-Sheet 4 Filed Jan. 7, 1965 i LP Nov. 7, 1 967 R. J. DEMAISON 3,351,460 METHOD FOR PROLONGING THE LIFE OF REFRACTORY LININGS IN FURNACES OF THE KALDO, LINZ-DONOWITZ, DEMAY OR BASIC OR ACID CONVERTER TYPES 5 Sheets-Sheet 5 Filed Jan. 7, 1965 INVENTOR. P J fifmw/so/v A; ORNEYS.

United States Patent 3,351,460 METHOD FQR PRQLDNGXNG THE LIFE OF RE- FRACT URY LENTNGS IN FURNACES OF THE KALDD, LiNZ-DONOWITZ, DE MAY 0R BASIC 0R AtIID CUNVERTER TYPES Raymond J. Demaison, Bronx, N.Y., assignor to Quigley Company, inc, a corporation of New York Filed Jan. 7, 1965, Ser. No. 424,071 13 Claims. ((Ii. 75-69) ABSTRACT OF THE DISCLOSURE Spraying upon the furnace linings a series of protective coatings of refractory material in wet slurry form according to a programmed schedule of alternate steel producing operations and lining spraying operations, the latter being performed by temporarily discontinuing the steel producing operations for repeated time intervals of sufficient duration to apply the coatings in amounts sufficient to prevent failure of the linings until relining becomes necessary.

This invention is directed to a method of maintaining against progressive deterioration the flame exposed refractory surfaces of high temperature furnaces of the basic oxygen type, such as the Kaldo, Linz-Donowitz, De May, and basic or acid converter type, while the furnace is at or near its operating temperature.

The invention of the Linz-Donowitz steel making pro esses has brought about a revolution in steel making throughout the world. Oxygen steel making did not become a possibility until cheap tonnage oxygen became available at least as early as 1930. Even with the oxygen tonnage being available, oxygen steel making did not become a reality until the successful completion of the intensive research and development program undertaken after World War II by Voest at Linz, Austria. The initial experimental work at Linz was, of course, directed to the type of iron ore available in Austria, but the versatility of the process has been thoroughly established by its adoption throughout the world.

The basic .advantages of the process, together with its versatility in regards to types of steel that can be produced and the raw materials used therein, has led to a world wide growth and use of the Linz-Donowitz process. Another dimension has been added to the versatility of the Linz-Donowitzprocess. There has long been a desire to increase the amount of scrap metal, and in some cases iron ore, which could be charged into the furnace. This would make possible a decreased dependence of the pro ess on the necessity of having hot metal available and also make it possible for the steel producers to take advantage of the fluctuating scrap metal markets. With this in mind, an investigation was undertaken to determine the feasibility of finding a substitute for the heat supplied by the hot metal. Subsequent tests, using a preheated furnace and charging the furnace with 100 pct. solid material and adding thereto about 5% to by weight of coke and then blowing the vessel with pure oxygen, have definitely shown that it was technically feasible to produce steel from a solid charge in a Linz-Donowitz furnace.

The Linz-Donowitz and the basic oxygen converters normally oxidize most of the CO to CO outside the furnace with a resulting loss of available exothermic heat that could be utilized to melt higher percentages of scrap. Burning carbon to CO produces at least three times the heat of burning carbon to CD only. The basic oxygen converters have in some instances realized this potential heat source as evidenced by the practice of positioning the furnace more towards the horizontal during start ups of cold furnaces or whenever a cold heat was apparent.

One of the first methods employed on a production scale to take advantage of burning most of the CO to CO inside the furnace, along with the use of pure oxygen lancing, is the rotating converter developed by Professor Bo Kalling and his associates and placed in full scale operation in May 1956 at Domnarvet, Sweden. A rotating concentric cylindrical furnace is used and is inclined at 17 (degrees) from the horizontal so the melt will cover at least half of the back wall, and it is rotated at speeds up to 30 r.p.m. The angle of inclination increases the productive capacity of the furnace and exposes more of the lining to the cooling effect of the mass of metal during rotation. The high speed rotation provides a greater degree of slag to metal contact than does stationary converters and a slag is formed earlier herein than in other processes to result in the rapid elimination of phosphorus and at the same time result in a low loss of iron to the slag.

The rotor process of De May is similar in operation to the Kaldo process and the reactions achieved therein and the results obtained therefrom are therefore similar.

The basic converters are of two types, one top blown and the other bottom blown. The furnaces are tilted and loaded with hot metal and/or scrap as desired. The furnace is then moved to a-vertical position and the oxygen and/or air and steam is blown in either from the top by means of a lance or upwardly through the molten metal contained therein by means of holes contained in the bottom of the furnace. When the metal has reached the desired stage and the elements therein are satisfactory, the furnace is again tilted and the heat poured by means of a tap hole provided in the converging neck of said furnace. In some instances, water is sprayed onto the slag to congeal it and prevent it from running off through the tap hole.

The foregoing short descriptions of the processes now being used to produce steel have been given to make clear the great differences in conditions that the refractories used in these new processes are subjected to, in order that the disclosures of the instant invention may be more readily understood and appreciated. In the case of the basic oxygen furnaces and basic converters, the refractories most used are tar-bonded shapes or fired shapes impregnated with tar or pitch to seal the pores thereof to prevent the ingress of moisture. In some instance, also, in the basic oxygen furnaces, particularly the Kaldo furnaces, electrically fused cast shapes are being used. The primary problem encountered in these furnaces is the erosion and wear taking place as the furnaces are loaded with scrap and moved during a heat, While the secondary problem is the rapid and wide variations in temperatures encountered with the extremes being produced on oxygen injection. A still further problem is the excess iron oxide formed in the slag during oxygen blowing with said slag also causing serious erosion of the lining.

It might also be noted here that the instant invention may be used on electric furnace linings as well as the linings of other furnaces to allow a greater number of heats to be produced during any one campaign.

The primary object of the invention is to insure a longer life to the refractory lining than could ordinarily be expected under the extreme operating conditions encountered, the net result being to bring down the lining cost per ton of steel produced and prolong campaigns.

Another object of the invention is to place on the flame exposed surfaces of the refractory lining, while it is at or near operating temperature, a protective coating which will prevent the deterioration of the parent lining and which will also be of such stability as to resist the erosion due to the movement of the hot metal and slag across the face thereof and, in addition, resist the abrasion from the additions of scrap metal to the furnace.

Still another object of the invention is to place on the flame exposed surfaces of the refractory lining coatings which will be compatible with the lining and with each other and still be of a greater refractoriness and resistance to higher temperatures than the linings themselves.

And still another object of the invention is to provide suitable equipment, such as spray pipes with suitable spray nozzles and suitable supports arranged to be thrust into the furnace, to spray the material onto the flame exposed faces of the refractory linings in layers or coats and thus furnish the means for protecting said linings. Where extremes of temperature are encountered the spray pipes and supports may be water cooled to insure their continuity of operation.

A still further object of the invention is to operate a series of furnaces of any type whether Kaldo, Linz-Donowitz, electric or basic or acid converters on a preset program of production and rehabilitation in order to insure the continued operation of said furnaces over a much longer period of time than has heretofore been possible so as thus to increase the steel production for any given campaign.

The primary concept of the invention is to insure the production of greater tonnages of metal from any single furnace during any one campaign regardless of the type of unit or the linings employed therein.

In the Linz-Donowitz units, which are normally lined with a tar dolomite brick or with a burnt dolomite brick and even in some cases with chromite bricks, the linings are varied in thickness depending upon the Wear pattern encountered, such as the charging side which has a higher abrasion resistant lining. In extreme cases, the normal linings have had a life of 250 to 300 heats during any one campaign, but this is extraordinary as the normal average life is around 200 to 225 heats.

In the LinZ-Donowitz type of unit, the refractory life is controlled by the following enumerated factors:

(1) Residual slag with varying amounts of active ingredients contained therein and such slag remaining in the furnace during temperature and analysis check and tapping, after which the slag is given increased viscosity for coating the charging side by adding burnt lime during the tapping to increase the viscosity, then draining the slag from the charging side to thus coat the refractories on this side of the furnace.

(2) Hot repairs. Tar dolomite material used to make repairs at specific points of repairs.

(3) Control of temperatures at the end of blowing to within :10 C.

(4) The holding of the hot metal in the furnace while obtaining the chemical analysis from the laboratory.

(5) Control of basicity and amount of slag by controlling the amount of lime to thus control the amount of silica in the metal and, in addition, controlling the amount of slag. Resulting in the iron content of the slag being kept as low as possible.

(6) Regulation of the lance height during blowing predicated on the number of heats of the furnace.

(7) Exercise care in the selection and loading of the scrap metal into the furnace to prevent extreme abrasion.

It can readily be seen that the life of the lining of the furnace can and will definitely be affected by the above stated factors. There are still other factors which may be involved as will be disclosed hereinafter.

The same factors as enumerated above also apply pretty much to the basic and acid converters.

In the Kaldo process, in contrast to the basic or acid converter and the Linz-Donowitz processes, oxygen operates essentially through the medium of the slag. The latter, lime saturated but still rich in iron oxide, enriches the metal upon contact. Naturally the mechanical agitation that is used and produced by furnace rotation produces rapid interaction between the hot metal and slag. In the normal operation of a Kaldo unit, several means are used to control the course of the refining operation: First, with a constant lance position and an increased oxygen input, the selective action of the jet can be displaced to the benefit of the metal bath and at the expense of the slag, resulting in dephosphorization, while a reduced oxygen input favors dephosphorization. The same results may be achieved by changing the lance position while maintaining a constant oxygen input. The closer the lance is to the bath the greater the rate of decarbonization, while the further away the lance is to the bath, the more dephosphorization takes place. The other variable used in controlling furnace operation is the speed of rotation of the vessel. A high rate of rotation exposes more of the metal surface to the direct action of the oxygen while the slag is being swept along the walls of the furnace. In this operation, two separate reactions take place simultaneously to, first, cause the slag to lose some FeO through the reduction of the metal-slag contact and, second, the oxygen acts in part directly on the bath to result in greater decarbonization than dephosphorization. A low rate of rotation, on the other hand, causes the slag to absorb oxygen and thus oxidizes more iron from the bath to thus eliminate phosphorous at the metal-slag surface. In retrospect, a slow rate of rotation favors dephosphorization while a high rate of rotation favors decarbonization. Here again it can readily be seen that the above stated facts will affect lining life.

The above description of the two major methods of producing steel today in furnaces clearly shows the variables that are encountered and that will affect the life of the lining of the furnace. In addition, it must be remembered that the initial charge is scrap metal and that subsequently, molten metal is added, and slag is formed, all of which adds to the wearing pattern of the refractory lining of said furnace.

It has been discovered that by pursuing the following procedure the life of a new lining in a furnace of the types described, may be greatly prolonged and in many instances up to from 500 to 600 heats or more, representing in effect the doubling or tripling of the normal life of the furnace lining:

(a) Operating the furnace under normal conditions for a substantially less than the normal or maximum number of heats per day for a selected number of days: for example, from 2 to 8 heats per day for from 6 to 25 consecutive days, but preferably 4 heats per day for 13 consecutive days, giving a total of 52 heats during this initial period. Spraying upon the furnace lining during this initial period, while the furnace is still at or near operating temperature, a series of successive protective coatings of refractory material to substantially increase the thickness of the lining for subsequent operations.

(b) Continuing the operation of the furnace under normal conditions for the full normal or maximum number of beats per day for a further selected number of days: for example, from 20 to 30 heats per day for from 4 to 10 consecutive days, but preferably 25 heats per day for 8 consecutive days, giving a total of 200 additional heats for this intermediate period.

(c) Continuing the operation of the furnace under normal conditions for a slightly less than the full normal or maximum number of heats per day for a further selected number of days: for example, from 16 to 28 heats per day for from 6 to 25 consecutive days, but preferably 20 heats per day for 13 consecutive days, giving a total of 260 additional heats during this final period and representing preferably a grand total number of 512 heats. Spraying upon the furnace lining during this final period, while the furnace is at or near operating temperature, an additional series of successive protective coatings of refractory material which will maintain the lining at sufiicient thickness to permit the furnace to be continued in operation throughout said final period. Prior to the spraying operations, the refractory material will be applied to patch the badly abraded, slag and hot metal eroded and spalled areas to restore the furnace lining to an even overall thickness.

In carrying out step (a) above, it is not necessary that the furnace be operated four heats per day for thirteen consecutive days nor is it necessary that the spraying operations during this initial period be carried out during each day of the furnace operation. The basic idea of this step (a) is to thermally condition the new brick lining and to build up thereon a series of successive protective coatings so as to substantially increase the thickness of the lining for operations during step (b) and step (c). A new lining might be seriously damaged if the furnace were operated under normal conditions for the full normal or maximum number of heats per day, bearing in mind that the material of the lining has not achieved complete thermal equilibrium or stability, but even after it does achieve such a condition, it would still be subject to abrasion, erosion and spalling during normal operations and hence would lose its original thickness in the absence of the protective coatings. These coatings are not applied continuously throughout the initial period to increase the thickness of the lining to the necessary extent, but they are applied in time intervals of sufiicient duration to permit the first coating to dry, set and fuse to the parent lining and each successive coating to dry, set and fuse to the preceding coating until the desired thickness of the lining has been achieved. The thickness of each successive coating is controlled according to the conditions under which the furnace is operated and the number of successive coatings is likewise controlled according to the con ditions under which the furnace is subsequently operated. However, there is a distinct advantage in applying the successive protective coatings at selected intervals during an initial period of operation of the furnace under norinal conditions. This is because the heat conditions existing Within the furnace during normal operation are differ ent from those that would exist if the lining of the fur nace were merely maintained at or near operating temperature throughout any given interval. In other words, during a normal furnace operation, the lining is not only subject to the abrasion which comes from loading the furnace with scrap material, but also subject to erosion and spalling which come from the pouring of the molten metal upon the scrap material as Well as the agitation of the molten metal due to the blowing of oxygen into the molten metal. Thus, the lining at one time is subjected to the maximum heat developed in normal operation and at another time to a lower degree of heat due to the temporary chilling of the molten metal under the conditions stated. It will not take too long to firmly condition the original lining and thereafter the applications of the protective coatings will enable it to withstand the severe conditions encountered because of increased thickness of the lining at the end of the initial period. Another desideratum are the time intervals followed in applying the successive coatings to cause them to dry, set and fuse as above stated to enable them to react with the furnace gases, coating by coating, until the total number of coatings has been applied. The total thickness of the coatings may reach as high as 6 inches and it can be appreciated that such a thick coating will not only increase the refractoriness of the lining as a whole but actually protect the parent brick lining against deterioration or spelling in subsequent operations due to the lower temperature gradients in the lining. And it goes without saying that the protection afforded the parent lining extends also to the shell of the furnace. In short, according to the present invention, this initial period, desirably 4 heats per day for 13 consecutive days, will actually control the total obtainable life of the lining.

In continuing the operation of the furnace as in step (b) above, the protective furnace lining will be able to withstand abrasion, slag and hot metal erosion and spalling which take place without the necessity of additional spraying. The number of days of furnace operation during this intermediate period could of course be varied according to the increase in thickness of the lining during the first period.

And further continuing the operation of the furnace as in step (c) above, the number of heats per day and the number of consecutive days comprising this final period may likewise be varied according to the increase in thickness of the lining during the first period and the reduction in such thickness taking place during step (b). The spraying operations during this final period may therefore vary likewise but, in any event, there should be applied to the furnace lining during this final period an additional series of successive protective coatings of refractory material which will maintain the lining at willcient thickness to permit the furnace to be continued in operation throughout said final period. The time intervals of coating applications, as in step (a), should be of sulficient duration to permit the first coating applied to the lining after step (b) to dry, set and fuse to the worn lining and each successive coating to dry, set and fuse to the preceding coating until the desired thickness of the lining has been achieved. The aim in this final period is to maintain a uniform maximum thickness of the furnace lining at the wear pattern area, so that the spraying operation should preferably be performed during each days operation of the furnace.

It is possible to resurface the worn, spalled, abraded or eroded areas of the linings with a compatible refractory material which will adhere to the parent refractory lining and become a part thereof so as thus to allow the furnace to operate over prolonged periods and increase appreciably the number of heats in any one campaign. This can be accomplished by the use of a preconceived plan predicated on the rate of loss of the thickness of the lining during any given number of heats to control the lining thickness as circumstances may demand. The plan may be arranged to either run the furnaces for a few heats each day and replace the abraded, eroded and spalled material daily in small increments or the furnaces may be run for a greater number of heats per day and replace the abraded, eroded and spalled material in larger increments daily to result in days with no replacement to thus allow the operation of the furnace to be scheduled as desired taking into account the daily number of heats and tonnage output, the Wear pattern resulting from the heats put on the furnace daily, the rate of daily replacement of refractory material on the lining including the building up of the wear pattern areas as Well as overall build up, and the total number of heats desired on the furnace lining per campaign. It has been ascertained that, in each of the specific types of furnace aforementioned, a definite wear pattern will usually be established during normal operation and it is therefore possible to apply a slurry of refractory material on the affected areas to build them up while the furnace is heated to build up the lining to its original thickness or of even greater thickness.

The following is an illustration of a program developed to carry out the invention:

Start with a new refractory lining in one furnace and proceed with a schedule worked out for the number of furnaces being activated and based upon the number of heats per day necessary to produce the desired daily tonnage. The schedule is to be so arranged as desirably to always run a furnace in step (b), which means that one furnace will supply the maximum daily tonnage while another one is relined, and the other steps so arranged that the maximum daily tonnage will be jointly produced with the newly relined furnace supplying the smaller part of the tonnage. Thus, taking the preferred example:

Days of Heats per Total No. Notes Campaign Day of Heats Step(a) 4 4 4 8 4 l2 4 16 4 2i) 4 24 4 23 4 32 4 36 4 4O 4 44 4 4S 4 52 Step (b) 25 77 25 102 25 127 25 152 25 177 25 202 25 227 25 252 Step(c) 20 272 20 292 20 312 20 332 20 352 20 372 20 392 20 412 20 132 20 452 20 472 20 492 20 512 1 Shooting periods of about 1 to 3 hours per day. 2 Shooting periods of about 2 to 4 hours per day.

It will be evident from the foregoing schedule that the total time elapsing in the steel producing operations before relining of the furnace is very much greater than the total time elapsing in the lining spraying operations, whereby a maximum steel production may be obtained during the prolonged life of the lining.

The schedule is self-explanatory and is based on the fact that one furnace must always be in operation and wherever possible a safety factor should be worked in to insure constant production. The normal object of the spraying programs as depicted under Notes 1 and 2 is to keep the linings in repair and of sufiicient thickness to preclude their failing until more than 500 heats have been accomplished. It has been ascertained that, in normal operation of the furnaces, about A" of the lining or sprayable material placed thereon is removed every 7 or 8 heats. The above scedule has been worked out and is now being used at several of the larger steel plants with very good success.

The refractory material used to mix with water to form the sprayable slurries will in the main depend on the type of lining used in the furnace and the mode of operation thereof. In the main, they will be chrome magnesite, magnesite-chrome compounds and straight magnesite. In all instances, the refractory compositions will contain suitable binders, suspension agents, and dispersion agents to insure the retention of the refractory material upon the surface of the hot refractory lining.

As before stated, the spraying is started with the linings at or near operating temperatures and the refractory material is applied in layers or coatings; and when in any furnace, after applying several layers, the lining begins to lose its redness, a gas torch is used to bring back the lining to its normal operating temperature. The loss of redness simply means that some heat has been used to dry out the layers of refractory material while some is lost in radiation, but the loss is not sufficient to cause a violent drop in the temperature of the center of the lining which could cause spalling. The same is true in reverse, in'that in the reheating of the lining the heat of the center is still sufficient to allow the refractory material on the face to be brought up to operating temperature without causing spalling.

The normal patching repairs will be made during the step (c) cited above and will be accomplished as follows:

(1) Fill up the normal wear pattern areas as they occur to somewhere near the normal thickness of the lining, layer on layer, with heating by torch if necessary;

(2) Or apply in one heavy layer and introduce hot slag over the patched area to assist in the baking and to protect the surface during the next heat;

(3) Then apply the refractory coatings to the overall surface of the lining.

In this manner, the lining may be kept at or near a given uniform thickness to allow over 500 heats .or more to be obtained.

In the normal operation of a plant, various situations will be encountered which will necessitate shutting down one furnace and using a second one to carry on and supply the minimum daily output. The blast furnaces may have to be shut down for cleaning and relining and it is also possible that the oxygen plant may be wholly or partially shut down for normal maintenance and repairs. It is these situations which will require a revised schedule but under no consideration will they cause any problems with said schedules as they can easily be changed and so not interfere with the minimum daily output of steel under these conditions.

The schedule divulged above is predicated on a particular operation of two furnaces in the field and the number of days in each step may be varied to suit the particular maintenance conditions and production schedules in each individual case. In this way it is possible to arrange the schedules so that they overlap and will allow one furnace to be relined while the other is carrying on somewhere near the beginning or center of a campaign to thus insure the minimum production needed from the shop. In the same manner, the basic schedule may be used to work out a continuous production schedule using three furnaces to thus keep two of the furnaces continuously on stream with one furnace down for relining. The normal down or relining period is approximately from 5 to 7 days in this particular instance and unless some defect is found in the shell of the furnace this time can be adhered to and the schedules built around it. If desired, an additional day or two may be incorporated in the schedule and it will be noticed that there are 8 days shown in step (b) above, which means that there are 5 to 7 days for the relining of the furnace with 1 to 3 days as a safety period.

In the accompanying drawings:

FIG. 1 is a cross sectional view of a basic oxygen furnace of the Linz-Donowitz type in a position tilted to the left for charging with steel scrap;

FIG. 2 is a cross sectional view of the furnace shown in FIG. 1 in the same tilted position but showing the addition of the hot molten iron;

FIG. 3 is a cross sectional view of the furnace shown in FIG. 1 but in a vertical position for the adding of slag forming materials, such as powdered limestone, etc.;

FIG. 4 is a cross sectional view of the furnace shown in FIG. 3 in a vertical position for blowing with oxygen and showing the water-cooled hood and oxygen lance;

FIG. 5 is a cross sectional view of the furnace shown in FIG. 4 but in a position tilted to the right for pouring the molten steel into a ladle;

FIG. 6 is a cross sectional view of the furnace in a horizontal position and tilted to the right for effecting repairs to the lining and showing in addition a cross sectional view of the floor and spraying apparatus in reference to the furnace;

FIG. 7 is a cross sectional view of a basic oxygen furnace of the Kaldo type and clearly shows the various positions assumed by the furnace during the operation cycle; and

FIG. 8 is a cross sectional view of a basic oxygen furnace and shows the lining and the trunnions upon which the furnace is tilted during operation.

Referring to FIG. 1 in particular, the furnace 1% with its lining 11 is tilted at a suitable angle for loading the steel scrap l2 thereinto from the body 13 mounted on the car 14. It will be noticed that the lining 11 of the furnace will be seriously abraded on the loading side as indicated at the area 15, thus giving rise to the first area to be repaired in order to keep the furnace in operation for longer periods of time. In some instances abrasion resistant bricks are installed in this area to keep this abrasion to a minimum amount.

FIG. 2 shows the hot molten iron 16 being poured over the scrap 12 from the ladle 17. There is little or no abrasion or erosion from the addition of the hot metal as it is poured over the scrap.

FIG. 3 shows the addition of the slag forming materials, such as powdered limestone 18, from the overhead chute 19. Here again there is little or no erosion or abrasion from the limestone, since it is in fine grained form.

FIG. 4 shows the furnace fitted with the water-cooled hood 20 which is equipped with a duct for leading the hot gases into a suitable precipitator for removing the solid particles contained therein. The hood 20 is fitted with the oxygen lance 22 so arranged as to blow the oxygen downwardly onto the molten metal and scrap. The shell 21 of said lance is arranged for the circulation of cold water therethrough to thus protect said lance against deterioration from the high heat developed in the furnace. In this operation, due to the high heats encountered and the boiling action of the hot metal and slag therein, there is a definite wear pattern established. Thus, the lining 11 of the furnace 10 is eroded at four definite areas as indicated at 25, 26, 27 and 28, and, strangely enough, the wear pattern at 25 and 27 is not always in circumferential form but occurs at 2, 4, 8 and 10 oclock positions on a section taken through the furnace with the smaller included angles being on the center line of the tilting mechanisms. The wear patterns at 25 and 27 do not occur in a vertical line but are inwardly inclined and are caused by the hot metal and slag when the furnace is in the tilted position. There is also a serious wear pattern established at 11a at the knuckle where the bottom lining and cylindrical wall lining are separated and the space therebetween is rammed with suitable material.

In this type of furnace, there is no rotation but only the tilt, so that there can be no confusion as to the position of the wear patterns. The wear pattern at 26 and 23 more or less is a continuous circumferential wear pattern as long as furnace operation variables are held constant and is caused by the erosion and spalling under the high temperatures encountered during the blowing period. In this type of conversion of iron to steel, it is not unusual to tap a heat in from 50 to 60 minutes from time of starting to load with scrap and hot metal, which fact definitely indicates that there is a much greater movement of the hot metal taking place in the furnace than would be encountered in an open hearth furnace.

FIG. 5 shows the molten metal 30 being poured into the ladle 32 resting on the car 33. The furnace is tilted so that the slag line 34 remains above the tap hole opening 35 to thus prevent the pouring of any of the slag out of the furnace with the steel. The complete pouring and emptying of the furnace is accomplished by simply tilt ing the furnace a little more until all the metal has run out. In some instances, cold water is sprayed on the slag to congeal it before pouring to insure that no slag is poured. Here again there is little or no erosion taking place in the furnace proper but there is considerable erosion of the tap hole which necessitates its repair quite often in order to insure proper pouring of the heat.

FIG. 6 shows the furnace ltl in a horizontal position tilted to the right for effecting repairs to the lining l1 and also shows a cross sectional view of the floor 36 in reference to the furnace. In addition, it shows the boom 37 with the supply pipe 38 mounted on the top thereof and with the spray nozzle 39 aifixed to the pipe. The boom is pivoted at 4ft, where it extends through the shield 41, to allow it to be tilted and thus spray the entire interior refractory surface of the furnace lining. The shield 41 contains the window 42 of heat resistant glass to allow the operator to direct the spray onto the worn, eroded, abraded and spalled areas. The shield is also formed of a steel plate of suitable thickness and lined with an insulation material either in brick or bat form, to keep the heat away from the operator. Said shield is suitably mounted on the A-frame 43 to allow the whole unit to be moved forward or backwards as desired to thus position the boom with its spray nozzle. The rear end of the boom 37 is weighted at 44 to counterbalance its forward inwardly extending end; and, in addition, the chain hoist 45 is connected by cable 46 to the extension 47 on the rear end of said boom to allow for vertical movement once the boom is in the furnace. The A-frame 43 is fabricated of aluminum or steel and, being light and equipped with suitable wheels, can be readily moved on the floor 36 to position the boom within the furnace as desired. In some instances, the boom may be water-cooled in order to allow it to be used for longer periods of time in the furnace. It is also possible to water-cool the supply pipe 38 and mount it for rotation about its axis.

The sprayable refractory material in suitable dry or slurry form is fed to the supply pipe 38 and spray nozzle 39 by means of the hose 48 which leads from a mixer capable of delivering the refractory material in either form as desired. In some instances, where dry refractory material is fed to the pipe 38, water may be mixed therewith by adding a 45 mixing nozzle at the point where the hose joins the pipe, as shown for example in copending application Ser. No. 402,203, filed Oct. 7, 1964.

It is also possible to use the boom for taking wear pattern measurements and also thickness measurements of applied coatings to allow complete checking of all phases of the operation.

The A-frame 43 may be dispensed with and the boom 37 mounted on a car running on rails used by other cars for various purposes. The boom can also be mounted on a set of cross rails aflixed to the top of the car and so moved back and forth while the vertical motion may be taken care of by hydraulic pistons and cylinders or even screw jacks if desired. The boom may even be sectionalized to allow it to be more readily transported from furnace to furnace or it may be folded up or back over itself. The boom is to be made of stainless steel and may be water-cooled if desired for longer shooting periods.

FIG. 7 shows the various positions assumed by the Kaldo type basic oxygen furnace during the operating cycle. The hot metal and scrap loading position is shown at 51, the blowing and lime and ore adding position at 52, and the pouring position at 53. It must be remembered that in the Kaldo process the furnace 50 is rotated about its axis and hence a more even wear pattern is established on the surface of the refractory lining. Here again the mouth of the furnace is fitted with a watercooled hood swingably mounted with the water-cooled oxygen lance 22 and water-cooled jacket 55 and lime and ore charging means 54 mounted therein. The method of repairing the lining of this type of furnace is the same as the Linz-Donowitz depending on the type of program chosen. The furnace can be rotated to a horizontal position where the boom can be employed after the hood is removed.

FIG. 8 is a cross sectional view of a basic oxygen converter furnace Illa showing the lining Ila and the trunmon 60 upon which it is tilted during operations. The operation of this type of furnace is similar to the Linz- 1 i Donowitz and in the interest of brevity the procedure will not be repeated.

From the foregoing disclosure it can readily be seen that a complete method for prolonging the life of refractory linings in furnaces of the Kaldo, Linz-Donowitz, De May or basic or acid converter types may be chosen depending upon the number of heats desired during any one campaign. If there are two or more furnaces it will be possible to alternate their operation and insure a positive output at all times. The instant method is now being used in several of the larger installations of the major steel plants and has definitely proven its superiority to other methods and programs.

The normal furnace life has been from 175 to 250 heats during any one campaign. According to the present invention, the furnace life may be extended to from 450 to 500 heats or more, resulting in a greatly reduced refractory cost per ton of steel produced and insuring continuous production.

The refractory material used for the repair and coating of the furnace linings may be of any type so long as it is suitable and effective for the practice of the invention as herein described. However, reference is made to the three following patents owned by the assignee of the instant application as examples of suitable refractory materials:

No. 2,809,126, dated Oct. 8, 1957, wherein the coating composition consists primarily of chrome ore;

No. 3,093,496, dated June 11, 1963, wherein the coating composition consists of a mixture of chrome ore and magnesia but wherein the chrome ore predominates;

No. 3,093,497, dated June 11, 1963, wherein the coating composition consists of a mixture of chrome ore and magnesia but wherein the magnesia predominates.

Reference is also made to Patent No. 3,093,458, dated June 11, 1963, also owned by the assignee of the instant application, and wherein refractory compositions of dif ferent refractoriness are employed in building up a multiple layer coating.

Another refractory material which may be used for the repair and coating of the furnace linings is disclosed in the copending Dreyling et al. application Ser. No. 173,839, filed Feb. 16, 1962, now Patent No. 3,241,987, which material consists essentially of dead burned or fused magnesite containing certain binding and barrier materials.

The spraying apparatus herein disclosed is being made :the subject of a separate application, namely, application Ser. No. 453,688, filed May 6, 1965.

Different types of spraying apparatus may be employed in carrying out the process and reference is made .to the following patents all owned by the assignee of the instant application:

No. 2,700,535, dated Jan. 25', 1955; No. 2,997,244, idated Aug. 22, 1961; No. 3,114,536, dated Dec. 17, 1963.

Reference is also made to the following copending applications which also disclose further types of spraying :apparatus that may be used in carrying out the instant process:

Demaison application Ser. No. 319,001, filed Oct. 25, 1963, now Patent No. 3,248,093; Demaison application Ser. No. 383,416, filed July 17, 1964, now Patent No. 3,248,093; Demaison application Ser. No. 402,203, filed :Oct. 7, 1964, now abandoned in favor of pending application Ser. No. 642,984, filed Apr. 6, 1967.

What is claimed is:

1. A method for prolonging the life of the refractory lining of a furnace of the acid or basic converter type by spraying upon the furnace lining in its cylindrical barrel and conical top portions a series of protective coatings of refractory material in the form of a wet slurry which will adhere to said lining and become bonded thereto as it is applied, comprising the step of operating the furnace throughout the life of the lining according .to a programmed schedule of steel producing operations and lining spraying operations, the lining spraying operations being performed by temporarily discontinuing the steel producing operations for repeated time intervals of sufficient duration to apply the protective refractory coatings in amounts sufficient to maintain the lining at a sufficient thickness to prevent failure thereof until the relining of the furnace becomes necessary, the total time elapsing in the steel producing operations before relining of the furnace being substantially greater than the total time elapsing in the lining spraying operations, whereby a maximum steel production may be obtained during the prolonged life of the lining.

2. A method for prolonging the life of the refractory lining of a furnace of the acid or basic converter type by spraying upon the furnace lining in its cylindrical barrel and conical top portions a series of protective coatings of refractory material in the form of a wet slurry which will adhere to said lining and become bonded thereto as it is applied, comprising the step of operating the furnace throughout the life of the lining according to a programmed schedule of steel producing operations and lining spraying operations, the lining spraying operations being performed by temporarily discontinuing the steel producing operations for repeated time intervals of suificient duration to apply the protective refractory coatings in amounts sufiicient to maintain the lining against failure throughout .an initial period of furnace operation, the steel producing operations during said initial period being programmed to cause the establishment of a state of thermal equilibrium in the furnace lining only near the end of said initial period.

3. A method for prolonging the life of the refractory lining of a furnace of the acid or basic oxygen converter type by spraying upon the lining of the furnace a series of protective coatings of refractory material, comprising the following steps:

(a) operating the furnace during an initial period of time according to a programmed schedule of steel producing operations and of lining spraying operations, the steel producing operations being performed under substantially less than maximum daily furnace operating conditions and the lining spraying operations being performed by temporarily discontinuing the steel producing operations during said initial period for time intervals long enough to apply the protective coatings of refractory material in amounts sufficient to maintain the lining against failure during said initial period, and

(b) during a further given period of time operating the furnace under substantially maximum daily steel producing conditions without spraying the lining during this further period, the amount of refractory coating material applied to the lining in step (a) being also sufiicient to protect the furnace lining against failure during this second step (b).

4. A method for prolonging the life of the refractory lining of a furnace of the acid or basic oxygen converter type by spraying upon the lining of the furnace a series of protective coatings of refractory material, comprising the following steps:

(a) operating the furnace during an initial period of time according to a programmed schedule of steel producing operations and of lining spraying operations, the steel producing operations being performed under substantially less than maximum daily furnace operating conditions and the lining spraying operations being performed by temporarily discontinuing the steel producing operations during said initial period for time intervals long enough to apply the protective coatings of refractory material in amounts sufficient to maintain the lining against failure during said initial period,

(b) during a further given period of time operating the furnace under substantially maximum daily steel producing conditions without spraying the lining l3 during this further period, the amount of refractory coating material applied to the lining in step (a) being also sufficient to protect the furnace lining against failure during this second step (b), and

() during a subsequent period of time operating the furnace according to a programmed schedule of steel producing openations and lining spraying operations, the steel producing operations being performed under slightly less than maximum daily furnace operating conditions and the lining spraying operations being performed by temporarily discontinuing the steel producing operations during this subsequent period for time intervals long enough to apply the protective coatings of refractory material in amounts suflicient to insure against lining failure during this third step (c).

5. A method for prolonging the life of the refractory linings of two furnaces of the acid or basic oxygen converter type, which consists in operating concurrently two furnaces each according to the method set forth in claim 4 but pursuant to a schedule in which step (a) of one furnace coincides with step (c) of the other furnace and in which step (b) of one furnace coincides with the relining of the other furnace.

6. A method for prolonging the life of the refractory linings of high temperature furnaces of the acid or basic oxygen converter type which consists in operating two furnaces concurrently according to a programmed schedule which will insure a substantially constant maximum daily steel production at least equal substantially to the maximum daily steel producing capacity of one furnace when operated alone and which comprises the steps of operating one of said furnaces at a substantially maximum number of steel producing heats per day while the other one of said furnaces is being relined, and likewise operating the latter furnace after relining at a substantially maximum number of steel producing heats per day while the former furnace is being relined, and in the periods between the relining operations operating the two said furnaces alternately, one at a less than maximum number of steel producing heats per day, and the other also at a less than maximum number of steel producing heats per day, the total number of steel producing heats per day of both furnaces being at least equal substantially to the maximum number of heats per day of one furnace alone, and during said intervening periods between the relining operations, while the furnaces are temporarily out of steel producing operation but still maintained at or near steel operating temperature, spraying upon the linings of the two said furnaces a series of protective coatings of refractory material in amounts sufficient to prevent failure of said linings while the furnaces are in steel producing operation, the spraying operations upon the lining of one furnace being carried out during the steel producing operations of the other furnace.

7. A method according to claim 6, wherein one furnace after being relined is first operated during a given period of time at a substantially less than maximum number of steel producing heats per day before being operated at the maximum number.

8. A method according to claim 6, wherein one furnace after being operated at the maxi-mum number of steel producing heats per day during the relining period of the other furnace is next operated at a slightly less than maximum number before itself being relined.

9. A method according to claim 6, wherein one furnace after being relined is first operated during a given period of time at a substantially less than maximum number of steel producing heats per day and later, after being 0perated during the relining period of the other furnace at the maximum number of steel producing heats per day, is operated at a slightly less than maximum number before itself being relined.

10. A method for prolonging the life of the refractory linings of high temperature furnaces of the acid or basic oxygen converter type which consists in operating three furnaces concurrently according to a programmed schedule which will insure a substantially constant maximum daily steel production at least equal substantially to the maximum steel producing capacity of two furnaces when operated simultaneously and which comprises the steps of operating two furnaces each at a substantially maximum number of steel producing heats per day while a third furnace is being relined, then repeating this step for the relining of each of the other furnaces, and in the periods between the relining operations operating the three furnaces in rotation, one at a less than maximum number of steel producing heats per day and the other two also each at a less than maximum number of steel producing heats per day, the total number of steel producing heats per day of all three furnaces being at least equal substantially to the maximum number of steel producing heats per day of two furnaces when operated simultaneously at said maximum number, and during said intervening periods, while the furnaces are temporarily out of steel producing operation but still maintained at or near operating temperature, spraying upon the linings of the three said furnaces a series of protective coatings of refractory material in amounts suificient to prevent the failure of said linings while the furnaces are in steel producing operation, the spraying operations upon the lining of one furnace being carried out during the steel producing operations of the other two furnaces.

11. A method according to claim 10, wherein any one furnace after being relined is first operated during a given period of time at a substantially less than maximum number of steel producing heats per day before being operated at the maximum number.

12. A method according to claim 10', wherein any one furnace after being operated at the maximum number of steel producing heats per day during the relining of another furnace, is next operated at a slightly less than maximum number before itself being relined.

13. A method according to claim 10, wherein any one furnace after being relined is first operated during a given period of time at a substantially less than maximum number of steel producing beats per day and later, after being operated during the relining period of another furnace at the maximum number of steel producing heats per day, is operated at a slightly less than maximum number before itself being relined.

References Cited UNITED STATES PATENTS 405,392 6/1889 Bertnand 20 1,607,554 11/1926 Meyer. 1,675,735 '7/1928 Stohr. 2,124,865 7/1938 Winkler et al. 26430 2,358,652 9/1944 Nicholas 26430 3,093,458 6/1963 Demaison 264-30 FOREIGN PATENTS: 579,918 8/ 1946 Great Britain. 836,472 6/ 1960 Great Britain.

BENJAMIN HENKIN, Primary Examiner. ROBERT F. WHITE, DAVID L. RECK, Examiners. J. A. FINLAYSON, Assistant Examiner. 

1. A METHOD FOR PROLONGING THE LIFE OFTHE REFRACTORY LINING OF A FURNACE OF THE ACID OR BASIC CONVERTER TYPE BY SPRAYING UPON THE FURNACE LINING IN ITS CYLINDRICAL BARREL AND CONICAL TOP PORTIONS A SERIES OF PROTECTIVE COATINGS OF REFRACTORY MATERIAL IN THE FORM OF A WET SLURRY WHICH WILL ADHERE TO SAID LINING AND BECOME BONDED THERETO AS IT IS APPLIED, COMPRISING THE STEP OF OPERATING THE FURNACE THROUGHOUT THE LIFE OF THE LINING ACCORDING TO A PROGRAMMED SCHEDULE OF STEEL PRODUCING OPETRATIONS AND LINING SPRAYING OPERATIONS FOR REPEATED TIME INTERVALS OF SUFFICIENT DURATION TO APPLY THE PROTECTIVE REFRACTORY COATINGS IN AMOUNTS SUFFICIENT TO MAINTAIN THE LINING AT A SUFFICIENT THICKNESS TO PREVENT FAILURE THEREOF UNTIL THE RELINING OF THE FURNACE BECOMES NECESSARY, THE TOTAL TIME ELAPSING IN THE STEEL PRODUCING OPERATINS BEFORE RELINING OF THE FURNACE BEING SUBSTANTIALLY GREATER THAN THE TOTAL TIME ELAPSING IN THE LINING SPRAYING OPERATIONS, WHEREBY A MAXIMUM STEEL PRODUCTION MAY BE OBTAINED DURING THE PROLONGED LIFE OF THE LINING. 